Rotary mowers may have two or more cutter blades mounted to generally vertical shafts, with the cutter blades positioned under a mower deck. Rear discharge mower decks may utilize the “cut and throw” approach in which the blades throw cut grass clippings into a discharge chute which may be connected to a rear mounted collection container or bag.
Mower decks generate noise for a number of reasons. Turbulent air coming off each blade as it passes through the air under the deck creates a broadband sound. As each blade passes by geometric changes of the deck shell, it creates a tonal noise typically referred to as blade pass noise. The size of the “wing” or “lift” component of each blade is a large contributor to both turbulent and blade pass noise. The blade wings help lift the grass or vegetation off the ground surface to provide an even cut, and also help material flow (i.e., grass clippings) into a mower's material collection system. A large wing may improve the quality of cut and material flow, but also may create more noise. In recent years, there has been a greater need to reduce noise generated by grass mowing equipment. A rear discharge mower deck is needed that will provide an effective quality of cut and material flow, without increasing noise emissions.
Discharge chutes of rear discharge mower decks tend to plug up with grass clippings, especially while cutting heavy or thick grass. Additionally, grass clippings that are too small, and/or have sufficient mass, tend to accumulate in discharge chutes instead of being propelled through the chute into a collection container. A rear discharge mower deck is needed that has a discharge chute that is less likely to fill with grass clippings during use.
To help propel grass clippings through a discharge chute, fans or blowers have been proposed for use on grass mowing equipment. For example, U.S. Pat. Nos. 4,114,353, 5,224,327, 5,542,243, 6,192,666 and 6,675,566 relate to lawn mowers with fans to help blow clippings through a discharge chute into a hopper or grass catcher. Additionally, U.S. Pat. Nos. 5,873,225 and 5,960,616 relate to rear discharge decks positioned extremely close to the ground, with a radial fan formed integrally with the spindle of the cutting blade and opening near a discharge chute. U.S. Pat. No. 6,073,430 relates to a rotary mower having a fan chamber concentrically positioned over a cutting chamber to provide additional suction and to exhaust clippings through an exhaust passage over the deck.